192 ALASKAN GLACIER STUDIES
North America,1 in which he states that" the evidence that a general retreatof the glaciers of Alaska is still in progress is abundant, and in a few instances of quantitative value." In Alaska the only advances mentioned by Russell were the comparatively recent advance of part of the border of Malaspina Glacier near Ft. Manby, from which the ice had retreated 1500 feet in 1891 when observed by Russell, and the advancing Frederika Glacier of the Wrangell Mountains, observed by Hayes in 1891, and cited by Russell as "the only instance of an advancing glacier known on the west coast of North America." He concludes that "the data relating to both the fluctuations of glaciers and to climatic changes are inadequate for satisfactory comparison," and that "the growth of glaciers and the initiation and decline of glacial epochs, are caused by very gradual climatic changes which would only become conspicuous, as climatic changes are now studied, after the lapse of centuries."
Gilbert, after his glacier studies in 1899,2 when He mentions a few other advances and retreats not cited by Russell, concluded that the lack of parallelism between variations of glaciers and different groups of glaciers in Alaska whose disparities are of larger scale than those of the Alps, just as the glaciation is of larger scale, might not be explained by either of two prominent climatic hypotheses, to each of which there are difficulties of application because the glacial and climatic data are indefinite, and because in climatic units in Alaska there is no known unity of glacier variation. He felt, however, tha>t the explanation must be climatic rather than diastrophic and made a suggestion that "the combination of a climatic change of a general character with local conditions of varied character, may result in local glacier variations which are not only unequal but opposite." The climatic change postulated is a change in the temperature of the water of the Gulf of Alaska. With the water becoming warmer and all other factors affecting glaciation remaining unchanged, "the consequences would include:
1. A higher temperature for the air currents flowing from the gulf to the land.
2. A greater contrast in temperature between the coastal belt and the interior of Alaska, especially in winter.
3. Greater evaporation from the ocean and a higher humidity for the landward-flowing airóresulting from 1.
4. Greater precipitation on the mountains, especially in winteróresulting from 2 and 8.
5. A shorter annual period in which precipitation takes the form of snowóresulting from 1.
6. A (probably) lower ratio of snow to rainóresulting from 5, qualified by 4.
7. A higher snow line.
8. More rapid waste of ice and snow by evaporation and meltingóresulting from 1, 5 and 7.
Of these consequences, the increase of precipitation would tend to enlarge glaciers, while the lessened ratio of snow precipitation and the enhanced wasting would tend to reduce them.
Evidently a lowering of the temperature of the gulf water would be followed by the reverse consequences."
As is shown in other chapters of this book, there have been many other glacial advances
i Russell, I. C., Amer. Geol., Vol. IX, 1892, pp. 322-888; Glaciers of North America, Boston, 1896, pp. 146-159. i Gilbert, G. K, Harriman Alaska Expedition, Vol. HI, 1001, pp. 102-112.